Gas turbine engines (GTEs) produce power by extracting energy from a flow of hot gas produced by combustion of fuel in a stream of compressed air. In GTEs, a mixture of compressed air and fuel is burned in a combustor of the turbine engine. The resulting hot gases spin blades of a turbine to produce mechanical power. In a typical GTE, fuel injectors direct a liquid or gaseous hydrocarbon fuel into the combustor. Combustion of the fuel in the combustor may create temperatures exceeding 2000° F. (1093.3° C.). This high temperature in the vicinity of the fuel injector may lead to coking, and coke deposition, in liquid fuel conduits of the GTE. Over time, coking may lead to flow restrictions that adversely affect the operation of the GTE. In some fuel injectors, insulating chambers or shrouds may be disposed around liquid fuel conduits that are susceptible to coking.
U.S. patent application Ser. No. 13/477,819, filed May 22, 2012, titled “Fuel Injector with Purged Insulating Air Cavity,” assigned to the assignee of the current application, describes a fuel injector with an insulating air cavity around a liquid fuel gallery. In the fuel injector of the '819 application, a purge hole is provided to maintain a positive pressure in the air cavity and thereby reduce accumulation of fuel-air mixture in the cavity.